Citrus huanglongbing (HLB) reduces an affected orchard`s economic life. This work aimed to characterize yield loss due to HLB for different sweet orange cultivars and determine the relationship between disease severity and yield. Disease severity and yield were assessed on 949 individual trees distributed in 11 different blocks from sweet orange cultivars Hamlin, Westin, Pera and Valencia. In each block, plants showing a range of HLB severity levels and asymptomatic plants were selected. Total yield (weight of harvested fruit), mean weight of asymptomatic and symptomatic fruit, relative yield (symptomatic tree yield/mean yield of asymptomatic trees from the same block) and relative number of fruits (fruit number from symptomatic tree/mean number of fruits from asymptomatic trees from the same block) were determined. The weight of symptomatic fruit was lower than the weight of asymptomatic fruit, but the weights of asymptomatic and symptomatic fruit were not correlated with disease severity, indicating that the effects of HLB were restricted to symptomatic branches. The relationship of the relative yield with HLB severity can be satisfactorily described by a negative exponential model. The rates of yield decrease as a function of disease severity were similar for all assessed cultivars. A relative yield (up to 19%) was observed even for trees where disease severity was 100%. The strong linear relationship between relative number of fruits per tree and the relative yield per tree suggested that the yield reduction was due primarily to early fruit drop or lack of fruit set on affected branches.; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)

The objective of this work was to assess the spatial and temporal variability of sugarcane yield efficiency and yield gap in the state of Sao Paulo, Brazil, throughout 16 growing seasons, considering climate and soil as main effects, and socioeconomic factors as complementary. An empirical model was used to assess potential and attainable yields, using climate data series from 37 weather stations. Soil effects were analyzed using the concept of production environments associated with a soil aptitude map for sugarcane. Crop yield efficiency increased from 0.42 to 0.58 in the analyzed period (1990/1991 to 2005/2006 crop seasons), and yield gap consequently decreased from 58 to 42%. Climatic factors explained 43% of the variability of sugarcane yield efficiency, in the following order of importance: solar radiation, water deficit, maximum air temperature, precipitation, and minimum air temperature. Soil explained 15% of the variability, considering the average of all seasons. There was a change in the correlation pattern of climate and soil with yield efficiency after the 2001/2002 season, probably due to the crop expansion to the west of the state during the subsequent period. Socioeconomic, biotic and crop management factors together explain 42% of sugarcane yield efficiency in the state of Sao Paulo.; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico

The objective of this work was to assess the spatial and temporal variability of sugarcane yield efficiency and yield gap in the state of São Paulo, Brazil, throughout 16 growing seasons, considering climate and soil as main effects, and socioeconomic factors as complementary. An empirical model was used to assess potential and attainable yields, using climate data series from 37 weather stations. Soil effects were analyzed using the concept of production environments associated with a soil aptitude map for sugarcane. Crop yield efficiency increased from 0.42 to 0.58 in the analyzed period (1990/1991 to 2005/2006 crop seasons), and yield gap consequently decreased from 58 to 42%. Climatic factors explained 43% of the variability of sugarcane yield efficiency, in the following order of importance: solar radiation, water deficit, maximum air temperature, precipitation, and minimum air temperature. Soil explained 15% of the variability, considering the average of all seasons. There was a change in the correlation pattern of climate and soil with yield efficiency after the 2001/2002 season, probably due to the crop expansion to the west of the state during the subsequent period. Socioeconomic, biotic and crop management factors together explain 42% of sugarcane yield efficiency in the state of São Paulo.

Maize yield is affected by water availability, which varies with field topography. The analysis of yield data obtained in different field landscape positions allows the spatial patterns of crop yield to be identified and related to field attributes, helping the spatial management of fields to be improved. The relationship between distance to flow accumulation lines (DFL) and spatial variability of yield and grain moisture at harvest has already been identified in a previous work by the authors. The main objective of this study is to confirm the relationship between DFL and spatial variability of yield and grain moisture at harvest, and also to establish a relationship between a field hydrological attribute (flow density) and average yield and distance to nearest flow accumulation line. The study was conducted using data collected from three agricultural fields (30,40 and 60 ha) irrigated by centre-pivot systems, in Southern Portugal, over a 3 yr period from 2002 to 2004.Collected data were divided into data sets corresponding to nine classes of DFL. Total flow lines length (SFLL) was used to calculate flow density (Fd). Based on these data sets, the relationship between yield and grain moisture at harvest and DFL and flow density was analysed. Coefficients of determination were very high (significant R2 from 0.91 to 0.98) for almost every year of the experiment...

Maize yield data were collected in seven agricultural fields irrigated by centre-pivot irri-gation systems, in Southern Portugal, from 2002 to 2004. These data were then correlated with different primary and secondary topographic attributes. The attained correlation coefficients were used to evaluate the relationship between yield spatial variability and each individual topographic attribute. In this three-year period applied water was always lower than crop water requirements. The increase of applied water in 2004 resulted in an improvement in average yield and especially in yield spatial stability. Average yield showed a strong dependency on topography, with high correlation coefficients between yield and elevation and slope. It presented also a high correlation with topographic indices that reflect field water availability, such as the wetness index and distance to flow accumulation lines (DFL). The DFL index was the topographic index with higher correlation coefficients with yield. The negative coefficients of correlation between yield and DFL, attained in most fields in the three-year study period, show that, in general, yield increases with the decrease of DFL, i.e., with the increase of water availability. In undulating land areas flow lines are very abundant...

Precision agriculture techniques imply a spatial management of fields and to do so a good understanding of the spatial and temporal variability of yield is needed. Average yield data from seven irrigated maize fields were used to study the yield pattern considering the distance of plants to flow accumulation lines. It was found that there is a significant correlation between average yield and distance to flow accumulation lines (DFL). This correlation is best represented by a polynomial function. The most common shape of the yield pattern curve considering the distance to flow accumulation lines shows that there is an increase in average yield with DFL from 0 to 12.5–17.5 m. Near the flow lines the average yield presents lower values due to drainage problems causing plant growth problems. It was also observed higher yield variability near the flow lines. For higher distances from the flow lines there is a continuous decrease in average yield due to less water availability and other variations of soil properties.

Yield monitors commonly show that there are very large yield differences within a field
which often differ from year to year. Because our ability to estimate reductions in growth
and to quantify yield losses resulting from complex interactions and multiple stresses is
limited, it does not appear feasible to analyse yield variability using a point to point
strategy. For a farmer it is important to select parcels of land, or parts of a parcel, with
a high yield probability. To analyse the high yield probability zones the Rasch model is used
considering a multi-temporal yield data set. The Rasch measure for multi-temporal yield
data makes it possible to place on a continuum axis the yield samples considered in terms
of annual yield and vice versa. Using the Rasch measurement one can produce yield
potential probabilistic maps taking into account each sample coordinate. From a quantitative
point of view it is possible to find yield samples that do not support the model, or
which do not reach the expected levels. Positive and negative mismatches can be analysed
individually or according to a particular year yield. Thus, the Rasch model makes it possible
to systematise the data, making it an effective tool for making appropriate decisions
regarding areas with higher yield performance and greater stability over time. Also...

Precision agriculture techniques imply a spatial management of fields and to do so a good understanding of the spatial and temporal variability
of yield is needed. Average yield data from seven irrigated maize fields were used to study the yield pattern considering the distance of plants to
flow accumulation lines. It was found that there is a significant correlation between average yield and distance to flow accumulation lines (DFL).
This correlation is best represented by a polynomial function. The most common shape of the yield pattern curve considering the distance to flow
accumulation lines shows that there is an increase in average yield with DFL from 0 to 12.5–17.5 m. Near the flow lines the average yield presents
lower values due to drainage problems causing plant growth problems. It was also observed higher yield variability near the flow lines. For higher
distances from the flow lines there is a continuous decrease in average yield due to less water availability and other variations of soil properties.

The objective of this study was to assess the impact of genetic breeding on grain yield, and to identify the physiological traits associated to the increment in yield and their related growth processes, for wheat cultivars grown in Southern Brazil, in the past five decades. Seven wheat cultivars released between 1940 and 1992, were compared for physiological aspects associated with grain yield. Grain yield, biological yield, biomass partitioning, harvest index and grain yield components were also determined. The number of grains per square meter was more affected by plant breeding and was better correlated with grain yield (r = 0.94, p<0.01) than with grain weight (r = -0.39ns). The higher number of grains per square meter was better correlated with the number of grains per spike in the modern cultivars than in the older ones. The genetic gain in grain yield was 44.9 kg ha-1 per year, reflecting important efforts of the breeding programs carried out in Southern Brazil. Grain yield changes, during the period of study, were better associated with biomass production (r = 0.78, p<0.01) than with harvest index (r = 0.65, p<0.01).

Grain yield forms one of the key economic drivers behind a successful wheat (Triticum aestivum L.) cropping enterprise and is consequently a major target for wheat breeding programmes. However, due to its complex nature, little is known regarding the genetic control of grain yield. A doubled-haploid population, comprising 182 individuals, produced from a cross between two cultivars ‘Trident’ and ‘Molineux’, was used to construct a linkage map based largely on microsatellite molecular makers. ‘Trident’ represents a lineage of wheat varieties from southern Australia that has achieved consistently high relative grain yield across a range of environments. In comparison, ‘Molineux’ would be rated as a variety with low to moderate grain yield. The doubled-haploid population was grown from 2002 to 2005 in replicated field experiments at a range of environments across the southern Australian wheat belt. In total, grain yield data were recorded for the population at 18 site-year combinations. Grain yield components were also measured at three of these environments. Many loci previously found to be involved in the control of plant height, rust resistance and ear-emergence were found to influence grain yield and grain yield components in this population. An additional nine QTL...

This thesis presents results from two separate studies. First, the impact of bearer length on yield components within the canopy was investigated in season 2005/06, on a commercially-managed, mechanically-pruned vineyard of Vitis vinifera L. Cabernet Sauvignon in Coonawarra, South Australia. Pruning resulted in the retention of bearers with 1-7 nodes, with the weighted average bearer length being two nodes for the canopy. As bearers of one to five nodes in length were the most common, these were studied. Yield components (on a per shoot basis) were analysed according to the node position on the bearer at which the shoot arose. Both budburst and inflorescence number per node were highest at the distal node positions on each length bearer, even if the nodes were at the same positions from the base of the bearer and would normally be expected to have similar fertility. Budburst appeared to act by modifying inflorescence number per node based on the relative location of each node from the apex of the bearer. Shoots that arose from the most distal node positions had the highest flower number per inflorescence and berry number per bunch. Flower number per inflorescence was significantly higher on two-inflorescence shoots than single-inflorescence shoots. The relationship between bunch size and node position...

Genetic improvement of essential Myrtaceae based oil crops is vital to
the long-term health and profitability of Australian essential oil industries.
Improving oil yield and efficiency is an important part of maintaining the
competitive advantage that Australian industries currently hold over
international competitors. Over the last 20 years, gains in oil yield have
been made through the tea tree breeding programme, which has helped
the industry get to where it is today. This work needs to continue to
advance, for the health of the industry into the future. Using molecular
techniques to facilitate this is the best way forward for the industry.
To better understand how oil yield is controlled in both tea tree
(Melaleuca alternifolia) and York gum (Eucalyptus loxophleba) within
Australia, I first investigated whether gene expression had an effect on
oil yield in M. alternifolia. In this study I investigated the transcript
abundance of 13 genes (dxr, dxs2, dxs3, cmk, mcs, mct, hds, mvk,
hmgs1, pmd1, ippi1, ippi2 and gpps) in 48 individuals that varied in oil
yield. The expression of all genes in the pathway explained 87% (R2 =
0.87) of variation in oil yield, These result are important in that they show
that oil yield isnʼt just controlled by one or two genes in the biosynthetic
pathway...

The Magdalena River, a major fluvial system draining most of the Colombian Andes, has the highest sediment yield of any medium- sized or large river in South America. We examined sediment yield and its response to control variables in the Magdalena drainage basin based on a multi-year dataset of sediment loads from 32 tributary catchments. Various morphometric, hydrologic, and climatic variables were estimated in order to understand and predict the variation in sediment yield. Sediment yield varies from 128 to 2200 t kmK2 yrK1 for catchments ranging from 320 to 59,600 km2. The mean sediment yield for 32 sub-basins within the Magdalena basin is w690 t kmK2 yrK1. Mean annual runoff is the dominant control and explains 51% of the observed variance in sediment yield. A multiple regression model, including two control variables, runoff and maximum water discharge, explains 58% of the variance. This model is efficient (MEZ0.89) and is a valuable tool for predicting total sediment yield from tributary catchments in the Magdalena basin. Multiple correlations for those basins corresponding to the upper Magdalena, middle basin, Eastern Cordillera, and catchment areas greater than 2000 km2, explain 75, 77, 89, and 78% of the variance in sediment yield...

Plant arrangement that allow better plant distribuition in the area results in larger grain yield. This increase might be the result of diferential contribution of canopy strata for yield determination. The experiment was performed at Agronomic Experimental Estation of the Universidade Federal do Rio Grande do Sul, in Eldorado do Sul, Rio Grande do Sul, Brazil, in the 2000/01 growing season. The objectives were to evaluate grain yield and yield components by stratum of soybean canopy in different plant arrangements, under two water availability. Tested cultivar was BRS 137 (early, determinate), in no-till planting. Treatments arrangements were split-splitplot randomized complete-block design, with four replications. Water availability (irrigate and no irrigated), row spacing (20 and 40 cm) and population levels (20, 30 and 40 plants.m-2) were tested. Grain yield and yield components, by soybean canopy stratum, were determined in samples of ten plants, in sequence in the row, in each sub-subplot. Grain yield was incresead by irrigation and was detected interaction between row spacing and plant population. Plant arrangememnt of 20 cm row spacing and population of 20 plants.m-2 resulted in greater grain yield. There was a linear decrease in grain yield with the increase in population...

Field experiments were conducted in the growing seasons of 2000-2001 and 2001-2002 to investigate the effects of various commercial foliar fertilizers containing N, P, K and micro nutrients on yield and yield components of triticale. Yield and yield component values were different among years because of dry season. The results revealed that foliar treatments had significant positive effect on grain yield, spikelet number per spike, number of grain per spike, 1000 grain weight and harvest index in both years. The most effective foliar fertilizer on yield and yield components during drought stress was Zn-15, a chelated (EDTA) form of zinc. Both NZN and ZnSO4 increased grain yield of triticale under no stress conditions.